The present invention relates to a dielectric filter used in radio communications, and the like at high frequency band as microwave band; quasi-microwave band, and the like and a dielectric resonator used in the dielectric filter, and more particularly to a triple mode dielectric resonator in which three resonant modes are available in one dielectric block and a dielectric filter using the dielectric resonator therein.
Conventionally, a dielectric filter which providing a cut-off waveguide with cylindrical or rectangular parallelopiped dielectrics disposing successively therein and utilizing resonance of a cylindrical TE01 xcex4 mode or a rectangular TE11 xcex4 mode of dielectrics is utilized widely in filters requiring low loss and size reduction, because the dielectric filter has high unloaded Q and can be reduced in size easier than waveguide type filter (a first conventional example). A resonance of the mode is generated by an electric field repeating reflections at an interface surface of the dielectric resonator and the air. The resonant frequency of dielectric resonator is inversely proportional to the length of the resonator and square root of dielectric constant, so that the larger the dielectric constant is, the smaller the resonator is. And a magnetic field generated by the resonance excites a resonator on the next stage and the excitation corresponds to the coupling between stages of the dielectric filter. As a magnitude of the coupling is mainly determined by the distance between resonators, the farther the distance is, the weaker the coupling is. As adjusting means for the above-mentioned dielectric filter, a method of adjusting the resonant frequency by a screw in a direction orthogonal to the reflecting surface of the magnetic field or a method of adjusting the coupling between the resonators by a screw, and the like are adoptable.
And there is also a dielectric filter utilizing a dual mode dielectric resonator in order to achieve size reduction (a second conventional example). The above-mentioned dielectric resonator provides two resonance by one resonator, in which a cylindrical dielectric resonator is disposed in the center of a cylindrical waveguide by justifying the axes of the cylinders, for example, and two resonance (HE11 xcex4) generated in two directions orthogonal to the axes of the cylinders are coupled by disturbing the electromagnetic field of the resonance from the waveguide side using means as screws, and the like.
As the description about a first conventional example above, the resonant frequency of the resonator by a cylindrical TE01 xcex4 mode or a rectangular TE11 xcex4 mode of dielectrics depends on dielectric constant and the size of dielectrics and a resonator can be smaller when the dielectric constant gets larger, accordingly the simplest method of reducing size of the filter utilizing the dielectric resonator is to raise the dielectric constant of dielectrics.
However, as dielectrics with low dielectric loss used in microwave region generally has a characteristic that dielectric loss thereof increases as dielectric constant becomes higher, size reduction of the filter maintaining insertion loss low has a certain limitation. Further, as dielectrics with low loss as mentioned above is expensive, accordingly the filter becomes expensive when the filter provides more stages, that is, provides more dielectrics used therein.
And a filter relative to a second conventional example utilizing HE11 xcex4 dual mode dielectric resonator for size reduction has a problem that lots of undesired modes excited in the vicinity of pass band result in spurious characteristic deteriorated easily, because HE11 xcex4 is not the dominant mode.
On the other hand, for example, in the event that a dielectric filter used in microwave communications, and the like is composed, it is conventionally hard to reduce size and weight of a dielectric filter, because many resonators and each spaces between the resonators occupies large amount of volume and weight according to the requirement of one resonator for one resonance and space for coupling between each resonator. Therefore, there still is a problem that the dielectric filter is unavoidably composed complicated and large, even though it is a band pass filter using dielectric resonators of relatively small size.
Consequently, composing a dielectric filter using dielectric resonators capable of multiple mode resonance is proposed to realize a band pass filter with a very small and simple composition exploiting advantages in using dielectric resonators fully. For example, size reduction of a band pass filter having a double-tuned band characteristic by varying the resonant frequency of the two resonance modes to each other is proposed in unexamined Japanese Patent Publication No. Hei 7-58516, in which degenerate coupling of two resonance modes with respect to TE101 and TE01 xcex4 modes is disclosed (a third conventional example). And a multiple mode dielectric resonator capable of generating TM01 xcex4 mode and TE01 xcex4 mode which are generated on a surface parallel to each surface (x-y surface, y-z surface, x-z surface) in a rectangular coordinate system in a generally rectangular parallelopiped shaped dielectric block is proposed in unexamined Japanese Patent Publication No. Hei 11-145704 (a fourth conventional example).
However, it is still unavoidable that a dielectric resonator occupies a large amount of volume in a band pass filter requiring a resonator of multiple stages, even though the degenerate coupling of two resonance modes relative to the above-mentioned third conventional example as described in unexamined Japanese Patent Publication No. Hei 7-58516 is utilized. And even a triple mode dielectric resonator relative to the fourth example as described in unexamined Japanese Patent Publication No. Hei 11-145704 has a problem that the manufacturing process becomes complicated, because utilization of hybrid coupling of TM01 xcex4 mode and TE01 xcex4 mode which are orthogonal spatially requires the thickness of dielectric resonator to be adjusted to resonant frequency.
It is therefore a first object of the present invention to realize a dielectric filter capable of reducing the number of dielectric resonators to a large extent, aiming at size reduction and cost reduction and providing favorable out-of-band characteristic by incorporating the mode which has been undesired into the band and activating the mode as a portion of resonance necessary for filter characteristic exploiting advantages that unloaded Q of the dielectric filter by a cylindrical TE01 xcex4 ode or a rectangular TE11 xcex4 mode relative to a first and a second conventional examples is high.
And a second object of the present invention is to solve the problem of the above-mentioned third and fourth conventional examples and to provide a very small dielectric resonator with simple composition in spite of enabling a triple mode resonance and a dielectric filter using the above-mentioned dielectric resonator.
The present invention aims at size reduction of dielectric filter by using three resonant modes in one dielectric block in order to achieve a first object of the above-mentioned present invention. That is, in a block of a generally rectangular parallelopiped consisting of dielectric material, three resonant modes in a single dielectric block can be coupled by chamfering a ridge portion of the dielectric block and another ridge portion unparallel thereto.
That is, the dielectric resonator claimed in claim 1 is characterized in combining three resonant modes of the above-mentioned dielectric block by removing one ridge portion and another ridge portion unparallel thereto in a block of a generally rectangular parallelopiped.
It is apparent from physical symmetry characteristics that a rectangular TE11 xcex4 mode can exist in each of three orthogonal axial direction in a block of a generally rectangular parallelopiped. In a conventional dielectric filter using TE11 xcex4 mode or HE11 xcex4 mode, the filter is composed using only one or two resonance out of the above-mentioned resonance of three axial direction, while the rest of the resonance exerts a harmful effect as undesired resonance. In the present invention, the rest of the resonance is utilized positively so that one resonator acts as three resonators.
And a dielectric filter claimed in claim 2 is characterized in disposing at least one dielectric resonator claimed in claim 1 in a cut-off waveguide.
Because a small dielectric filter with low insertion loss can be manufactured by composing a filter in which one or more of the above-mentioned dielectric resonators are disposed in the cut-off waveguide.
Further, a dielectric filter claimed in claim 3 is characterized in disposing two or more of the above-mentioned dielectric resonators in the above-mentioned cut-off waveguide and providing means for partition consisting of electric conductive material between the above-mentioned dielectric resonators.
Because, in the event of using plural of resonators, it becomes possible to adjust the coupling of each mode between resonators properly, to take required coupling for the pass band characteristics and to form an attenuation pole out of the pass band by providing conductive partitions between each of the resonators.
And a dielectric filter claimed in claim 4 is characterized in disposing a metal rod contacting with the above-mentioned waveguide by one end parallel to a side surface of the above-mentioned dielectric resonator in a position away from the above-mentioned side surface by a predetermined distance, in which resonant frequency of each resonance and the coupling between each of the resonance are adjustable depending on the length of the above-mentioned metal rod.
Because, a filter using a triple mode dielectric resonator according to the present invention is capable of adjusting resonant frequency and the amount of coupling by putting a metal rod as a screw from the cut-off waveguide parallel to the side surface of the dielectric resonator in the position away from the side surface of the dielectric resonator by a predetermined distance and occupying adjustable range of the filter widely by combining above-mentioned operation with conventional means for adjusting.
Incidentally, a dielectric filter claimed in claim 5 is characterized in further installing a resonator other than the dielectric resonator claimed in claim 1 in the above-mentioned waveguide as well.
Because, a small filter with an arbitrary number of stage can be composed by combining the triple mode dielectric resonator according to the present invention and resonators of dielectrics TE01 xcex4 mode or TEM mode by metallic conductor, and the like. Besides, out-of-band characteristics all over the filter can be improved by using a resonator with less undesired resonance or with undesired resonance located away from the necessary band as the above-mentioned combined resonator.
On the other hand, in the present invention, a dielectric resonator is composed of a dielectric block of a generally rectangular parallelopiped with three ridge portions chamfered thereof and TE01 xcex4 mode is generated on the electro-magnetically individual three surfaces of the above-mentioned dielectric block as claimed in claim 6 in order to achieve the above-mentioned second object of the present invention.
Incidentally, it is preferable for the above-mentioned dielectric block to be mounted in a cut-off waveguide of a generally rectangular parallelopiped as claimed in claim 7.
And a dielectric resonator claimed in claim 8 is characterized in having three surfaces of A1, A2, A3 (hereafter called surfaces A) formed by chamfering three ridge portions sharing an apex of the above-mentioned dielectric block and three surfaces of B1, B2, B3 (hereafter called surfaces B) adjacent to each of the surfaces A respectively, in which an angle between 40 degrees and 50 degrees, both inclusive, is offered by the surfaces A and B and an area ratio of the above-mentioned surfaces A with respect to the surfaces B stands between 1% and 200%, both inclusive.
Further, a dielectric resonator claimed in claim 9 is characterized in having three surfaces A formed by chamfering three ridge portions sharing an apex of the above-mentioned dielectric block, another three surfaces of Axe2x80x24, Axe2x80x25, Axe2x80x26 (hereafter called surfaces Axe2x80x2) formed by chamfering three ridge portions sharing another apex on a diagonal line of the above-mentioned point, another three surfaces of Bxe2x80x21, Bxe2x80x22, Bxe2x80x23 (hereafter called surfaces Bxe2x80x2) adjacent to each of surfaces A and surfaces Axe2x80x2 respectively and still another three surfaces of Cxe2x80x21 Cxe2x80x22 Cxe2x80x23 (hereafter called surfaces Cxe2x80x2) adjacent to each of surfaces A and surfaces Axe2x80x2 respectively, in which an angle between 40 degrees and 50 degrees, both inclusive, is offered by the surfaces A and Bxe2x80x2 or by the surfaces Axe2x80x2 and Cxe2x80x2 and an area ratio of the above-mentioned surfaces A with respect to the above-mentioned surfaces Bxe2x80x2 or an area ratio of the above-mentioned surfaces Axe2x80x2 with respect to the above-mentioned surfaces Cxe2x80x2 stand between 1% and 200%, both inclusive, respectively.
On the other hand, a dielectric filter claimed in claim 10 is a dielectric filter using a dielectric resonator, in which an angle between 40 degrees and 50 degrees, both inclusive, is offered by the above-mentioned three surfaces A or Axe2x80x2 and other three surfaces B or Bxe2x80x2 adjacent thereto respectively and the surfaces A or Axe2x80x2 and surfaces B or Bxe2x80x2 adjacent thereto respectively have three opposing surfaces of C1, C2, C3 (hereafter called surfaces C) or the surfaces Cxe2x80x2 and characterized in providing a feeding probe near the surfaces B and Bxe2x80x2, the surfaces Bxe2x80x2 and Bxe2x80x2, the surfaces C and Cxe2x80x2, or the surfaces Cxe2x80x2 and Cxe2x80x2.
And a dielectric filter claimed in claim 11 is a dielectric filter using a dielectric resonator having the above-mentioned three surfaces A formed by chamfering three ridge portion sharing an apex of the above-mentioned dielectric block, another three surfaces B adjacent to the above-mentioned three surfaces A forming an angle of 40 degrees through 50 degrees and three surfaces C opposing to the above-mentioned three surfaces B respectively, in which a feeding probe is provided on the surfaces B and surfaces C.
Incidentally, as a dielectric filter claimed in claim 12, an angle offered by direction p and pxe2x80x2 of the feeding probe with respect to the x, y, z axes of the above-mentioned dielectric resonator are variable within the range of xe2x88x9245 degrees through +45 degrees while in use.
And as a dielectric filter claimed in claim 13, frequency and attenuation generating the attenuation pole at a lower side band can be varied by varying a position for providing a feeding probe on the above-mentioned surfaces B and a position for providing a feeding probe on the above-mentioned surfaces C respectively.
Here, either of rod-type as claimed in claim 14 or loop-type as claimed in claim 15 is acceptable as the above-mentioned feeding probe.
Further, as claimed in claim 16, a dielectric filter capable of being applied to various kinds of application can be composed by mounting two or more of the above-mentioned dielectric resonators in the above-mentioned cut-off waveguide of a generally rectangular parallelopiped therein.